"Happy Heart" is a song written by James Last and Jackie Rae. Versions of the song Petula Clark and Andy Williams charted simultaneously in 1969 and had their best showings on Billboard magazine's Easy Listening chart, where Clark peaked at number 12 and Williams spent two weeks at number one.

The first recording of "Happy Heart" to reach the charts in Billboard magazine was an instrumental version by record producer Nick DeCaro that debuted on the Easy Listening chart in the March 15, 1969, issue and got as high as number 22 over the course of seven weeks. DeCaro had recently produced the albums Born Free, Love, Andy, and Honey for Williams, who recorded "Happy Heart" on March 8 of that year. Williams also performed the song for Clark's NBC television special Portrait of Petula that would air on April 7.

A full-page advertisement in the March 22 issue of Billboard with the headline The Latest Thing from Paris showed a pair of bare legs standing in cleated running shoes and described the rush that Clark and her record company were in to get a recording of the song out:

Last Monday. Petula races from Paris to Hollywood. She lives in Paris. She records in Hollywood. She races in with no suitcase. Just one song. A quick trip for just one short song? Not with the song Petula's holding. What Petula holds is probably the song of the year. That night, with arranger Ernie Freeman, Petula records "Happy Heart". By Tuesday morning [Warner Bros. executive Joe] Smith has "Happy Heart" all wrapped up and shipping. We, too, are off to the races. "Happy Heart" is, indeed, the latest thing. Right now, the guys from Warners're racing at you, with that latest thing. From Petula. Excited? Petula's "Happy Heart" beats at Warner Bros., who race to win.

The differences between the arrangements of the two vocal versions stood out for critics. Billboard described both of them in one capsule review, which also appeared in the March 22 issue. "Miss Clark's reading is soulful with a driving slow beat. Williams's, produced by Jerry Fuller, is a brighter tempo with much jukebox appeal as well."

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